1. The Field of the Invention
The present invention relates generally to anesthetic gas delivery devices. More particularly, embodiments of the present invention relate to an improved anesthesia mask for effective and reliable administration of anesthetic gases to animals.
2. The Prior State of the Art
It is generally acknowledged that administration of anesthetic to animals prior to and during surgery provides a variety of benefits, both to the animal and to the surgeon. In particular, the typical anesthetic sequence produces three desired results or effects in the animal. These three effects generally include: first, narcosis (animal is rendered unconscious); second, analgesia (the animal is rendered insensitive to pain) and suppression of reflexes; and third, muscle relaxation. Clearly, narcosis and analgesia provide a significant benefit to the animal since, as a result of these anesthetic effects, the animal suffers no pain and is unaware of the surgery taking place. Narcosis is important to the surgeon as well, since it allows the surgeon to further prepare the animal for surgery without harm to either the animal or the surgeon. Further, suppression of reflexes and muscle relaxation of the animal is important to the surgeon since it is obviously undesirable to have the animal""s muscles and limbs flexing and/or moving while the surgeon is attempting to perform a surgical procedure.
Generally, the first effect, narcosis, is produced via intravenous administration of anesthetic. The effects of analgesia and reflex suppression are required in order to prepare the animal for intubation (i.e., placement of an endotracheal tube in the animal) and are typically achieved by using a temporary means to briefly force anesthetic gas into the animal""s lungs and thereby place the animal in a deep state of unconsciousness. Upon achievement of analgesia and reflex suppression, the animal is then intubated for the remainder of the procedure. The final anesthetic effect of muscle relaxation is then achieved, and thereafter sustained, by connecting the endotracheal tube to a breathing circuit supplying the pressurized gaseous anesthetic.
While this anesthetic sequence is widely used and accepted, there are aspects of the associated equipment that remain problematic. One significant problem area concerns conventional masks used to introduce an anesthetic gas into the animal""s lungs to achieve analgesia and reflex suppression. Intubation and the related equipment present another source of problems.
Turning first to the anesthesia masks, significant problems exist with conventional masks which have yet to be satisfactorily resolved. The major, overarching problem is that there is no known anesthesia mask that is specifically designed for use with animals, particularly dogs and other animals with muzzles or similar facial anatomy. As a necessary consequence, veterinarians have been forced to resort to a variety of incomplete and unsatisfactory solutions. Typically, veterinarians have taken one of two different approaches.
Some veterinarians simply use an anesthesia mask designed for humans. Obviously, a mask that fits a human well is clearly unsuited for use with canine anatomy. Accordingly, it is difficult, if not impossible, to adequately seal a human anesthesia mask around the muzzle of a dog. Further, because of the significant differences between canine and human anatomy, it is virtually impossible to encompass both the nose and mouth of a dog with an anesthesia mask designed for use by humans. Improperly shaped and sized anesthesia masks permit anesthetic to escape and thus it is difficult, if not impossible, for the anesthetist to determine if the proper volume of anesthetic is being delivered to the animal at the proper rate. This is clearly problematic because an improperly or inadequately anesthetized animal may compromise the surgeon""s ability to perform the procedure. Likewise, the animal could suffer injury and possibly death if it is not properly anesthetized.
In an attempt to overcome the problems attending inadequately shaped and fitted anesthesia masks, anesthetists typically hold the mask in place in order to ensure the adequate flow and effective delivery of anesthetic that are required to induce a deep sleep in the animal. Generally, anesthetists are able to use this method effectively for only about ten minutes. Thus, surgical procedures lasting longer than ten minutes typically require intubation of the animal. As discussed in greater detail below, intubation introduces an additional set of problems, not the least of which are the logistics and expense involved with intubation.
Other veterinarians have moved a step further and attempted, with limited success, to modify human anesthesia masks to accommodate canine anatomy. While these modified anesthesia masks arguably represent an improvement over unmodified ones, problems remain. First, both time and expense are incurred in modifying human anesthesia masks to fit animals. Further, the functionality achieved by such modifications is modest at best. The surgeon or assistant may still have to hold the mask in place in order that the desired anesthetic effect can be achieved. Finally, the modified anesthesia mask is typically only suited for use with animals of the same size and anatomy as the one for which the mask was originally modified. Thus, while the modified mask may be somewhat effective for the particular animal for which it was modified, it is typically of limited utility where other animals are concerned.
In addition to modifying human anesthesia masks for use with animals, veterinarians have been forced to employ a variety of other primitive and generally ineffective equipment. Some of the other types of equipment currently in use by veterinarians include modified plastic containers, and anesthesia chambers constructed from modified fish tanks.
Another problem with conventional masks is that the animal""s mouth needs to be allowed to open so that the tongue can move to prevent the animal from choking. At least one other problem with known masks is that they are typically ill-suited to accommodate the instrumentation necessary to monitor the vital signs of the animal when the animal is in the deep sleep typical of the final step of the anesthetic sequence. This is problematic because vital sign feedback is critically important during the procedure. For example, one vital sign or parameter of particular interest is the oxygen content of the blood of the animal. Oxygen content monitoring, or oximetry, provides valuable feedback on the effectiveness of the anesthetic gas and provides early warnings of possible complications that may arise during the procedure. Finally, oxygen content monitoring provides direct measurement of the material condition of the respiratory system of the animal. One way of monitoring the vital signs of the animal is to attach a monitor to the tongue of the animal.
As suggested above, intubation is another problem area where anesthetizing animals is concerned. One of the difficulties with the use of endotracheal tubes concerns the resistance of the breathing circuit to which the animal is connected during surgery. It is generally acknowledged that friction between a flowing fluid (which broadly encompasses both liquids and gases) and the pipe or tube through which it moves, resists fluid flow and tends to decrease the velocity of the fluid as the fluid travels down the tube. It follows that the overall loss in velocity increases with the length of the tube. Further, it is well known that the volume of gas delivered through a tube of a given size is directly proportional to the velocity of the gas, so that a relatively lower velocity corresponds to a relatively lower gas delivery rate. In view of the foregoing discussion, it is clear that the addition of an endotracheal tube to the breathing circuit increases the resistance of the circuit and tends to diminish the rate at which anesthetic gas is delivered. Thus, an intubated animal has to work harder to breath than a non-intubated animal. This is particularly problematic in view of the fact that the animal already has a diminished breathing capacity due to the effects of the anesthetic.
There are other problems as well that are associated with the use of endotracheal tubes. These problems include, but are not necessarily limited to, complications such as tracheitis and laryngeal edema, accidental dislodgement of the tube, chemical tracheitis resulting from the disinfectants used for cleaning the tubes, and infections resulting from improperly sterilized tubes. Finally, intubation is time-consuming and expensive, thus it is desirable to minimize or eliminate the need for intubation to the maximum extent practicable.
Accordingly, what is needed is an improved anesthetic delivery device or mask for animals, and for canines in particular. Specifically, the anesthesia mask should have a shape well-adapted for use with animal anatomies and should be sufficiently large to permit the mouth of the animal to remain open slightly during the procedure to prevent the animal from choking as well as allowing instruments to be placed in and/or near the mouth and tongue of the animal. Further, the anesthesia mask should completely receive both the nose and mouth of the animal in the cavity, but should avoid contact with the eyes of the animal. Also, the anesthesia mask should provide for substantial sealing of the cavity when the nose and mouth of the animal is received in the cavity. Additionally, the mask should be self-adjusting so that a single mask will securely and reliably fit, without modification, a variety of different animal anatomies. Finally, the mask should be well-suited to cooperate with instrumentation for monitoring animal vital signs.
The present invention has been developed in response to the current state of the art, and in particular, in response to these and other problems and needs that have not been fully or completely solved by the anesthesia masks currently in use by veterinarians.
Thus, it is an overall object of the present invention to provide an anesthesia mask that is particularly useful, when used in conjunction with an anesthetic breathing circuit, for anesthetizing a variety of different animals.
It is a another object of the invention to provide an anesthesia mask that defines a cavity shape closely approximating the shape of the facial anatomy of an animal so as to ensure effective, adequate, and reliable delivery of anesthetic.
It is a related object of the invention to provide an anesthesia mask having a breathing circuit interface disposed substantially proximate to the nose of the animal, when received in the cavity, so as to effectuate efficient delivery of the anesthetic to the animal.
It is similarly a related object of the invention to provide an anesthesia mask suitably large to encompass the mouth of the animal, as well as the nose of the animal, so as to prevent escape of anesthetic gas from the mouth.
It is another object of the present invention to provide an anesthesia mask having a self-adjusting seal so as to securely hold and seal the mask, without modification, on a variety of different facial anatomies.
Yet another object of the present invention is to provide an anesthesia mask that can be quickly and easily put on an animal.
Finally, it is an object of the present invention to provide an anesthesia mask having one or more self-sealing ports through which instrumentation wires can be passed so as to permit monitoring of the vital signs of the animal without significantly compromising the seal of the anesthesia mask.
In summary, the foregoing and other objects, advantages and features are achieved with improved anesthesia mask for use in supplying anesthetic to a variety of different animal types. Embodiments of the present invention are particularly suitable for use as in conjunction with a pressurized-gas anesthetic breathing circuit.
In one embodiment, the body of the anesthesia mask defines a cavity that is substantially in the shape of an animal muzzle. The body of the anesthesia mask has a first end that is configured to interface with a breathing circuit and a second end that is open. The body of the anesthesia mask is cut away from the first end to the second end in an area extending between the nose of the animal and the back of the mouth of the animal so that the anesthesia mask encompasses both the nose and mouth of the animal and simultaneously permits ready placement of instrumentation on the tongue of the animal. In this embodiment, a resilient seal member is disposed across the open second end of the body of the anesthesia mask and is releasably engaged with the body of the anesthesia mask so as to permit ready removal and replacement of the resilient seal member. The resilient seal member has an aperture formed therein through which the nose and mouth of the animal are received into the cavity. When the nose and mouth of the animal are inserted into the cavity, the sides of the aperture are deflected and/or deformed to the extent necessary to permit ready entry. Once situated in the cavity, the nose and mouth of the animal are substantially sealed therein and securely held in place by the resilient seal member which, because of its resilient nature, substantially conforms to the shape of the nose and mouth of the animal.
These and other objects, features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.